Photo by Glenn Eckert
Birds of all species make many kinds of nests including mounds, cups, platforms and many more!
Photo by Seney Natural History Association, CC BY-SA 2.0, via Wikimedia Commons
In Alberta, cavity nesting is a common nesting technique. A cavity nest is a chamber typically created in a dead tree snag that the bird will hollow out to lay its eggs in. These birds are called Primary Cavity Nesters. Creating these nests are no small feat, as it may take the bird several days to a week!
However, some bird species that may be incapable of hollowing out the trees (or just lazy!) will take over these cavities after the primary cavity nesters are done. These birds are known as Secondary Cavity Nesters.
Primary Cavity Nesters
Pileated Woodpecker – Example of a Primary Cavity Nester, Photo by Glenn Eckert
Few species can excavate their own nests, including woodpeckers, trogons, and some nuthatches.
The nests are typically excavated on the underside of a tree branch, probably to make it less visible to predators and reduce rainfall into the nest. These cavity nesters have to be wary of predators cornering them and their young inside, so some species have adapted defenses. Red-breasted Nuthatches will spread sap around the entrance to their nests, and white-breasted nuthatches surround theirs with smelly insects!
Most species will only use the cavity once, which leaves it open for other species to use in following years.
White breasted nuthatch excavating a home! Photo by Glenn Eckert
Secondary Cavity Nesters
Secondary cavity nesters take advantage of abandoned cavities, or sometimes even kick other speciesout. Some of the common secondary cavity nesters include Mountain Bluebirds, Tree Swallows, House Wrens, and some owls. These birds will leave the cavity mostly the same except for some small amendments such as adding some fur, grass or moss to the excavated cavity. Other species will take advantage of cavities as well, including Northern Flying Squirrels.
Saw whet owls – A secondary cavity nester, Photo by Glenn Eckert